In such steam generators, after heating in the reactor core, the water of the primary circuit (hereinafter called "primary water") circulates in an inverted U-tube bundle to transfer its heat to the secondary circuit water (hereinafter called "secondary water"), in order to convert it into steam.
More specifically, the inverted U-tube of the bundle are arranged in parallel layers and their rectilinear branches traverse horizontal spacing plates ensuring the relative positioning thereof over most of the height of the bundle.
In the upper part of the bundle, i.e., in the intermediate, inwardly curved part of the tubes, the maintaining of the relative positioning between the tubes is maintained by antivibration bars. More specifically, at least one more or less open V-shaped bar is normally placed between each pair of layers of adjacent tubes to prevent the vibration of the tubes in the upper part of the bundle and which could result from the circulation of the water inside and outside the tubes. All the antivibration bars are interconnected beyond the bundle of tubes by connecting or jointing pins welded to the ends of the bars.
As is more particularly illustrated by U.S. Pat. No. 3,007,679, in a device for supporting the upper part of the bundle of tubes, the flying off of the assembly formed by the connecting pins and the antivibration bars is normally prevented by anti-fly-off clips fixed to the connecting pins and encircling some of the tubes positioned outside the bundle.
In such a structure, the anti-fly-off clips suffer from the disadvantage of interconnecting several tubes of the bundle, which creates stresses in case of differential expansions of the tubes, particularly if one or more of them are blocked or sealed during the life of the steam generator.